Ehvidence
Favorable Efficacy (RCT)

Nicotinamide for skin cancer prevention

Oral nicotinamide 500 mg twice daily vs. Placebo · for Nonmelanoma skin cancer (high-risk patients) · real-time analysis of 1 studies · updated 2026-05-29

In patients with a history of nonmelanoma skin cancer, oral nicotinamide (vitamin B3) for 12 months reduced new nonmelanoma skin cancers by about 23%, with similar reductions in basal- and squamous-cell carcinomas and in actinic keratoses. It is inexpensive, over-the-counter, and well tolerated, but the benefit fades once it is stopped.

Efficacy (RCT): Efficacy evidence on clinical outcomes. Effects are risk ratios with number-needed-to-treat where a baseline risk is available. Glossary →

Interpretation & tips

Outcomes are lesion rate ratios, so NNTs are per skin cancer prevented over 12 months—strikingly low here because high-risk patients get many lesions, and not transferable to average-risk people. The benefit disappears within months of stopping. Evidence is a single phase 3 trial; the basal-cell result was not significant and squamous-cell was borderline.

23% lower risk of new nonmelanoma skin cancers
Pooled RR 0.77 (95% CI 0.62–0.96) across 1 studies, 386 patients (random-effects, I² 0%).
0.77
Pooled RR
0.62–0.96
95% CI
1
Studies
386
Patients
2
NNT

Forest plot—New nonmelanoma skin cancers

ONTRAC (Chen) 2015 0.77 [0.62–0.96] Pooled (RE) 0.77 [0.62–0.96] 0.1 0.25 0.5 1 2 4 ← favors treatment favors control →

Study results—New nonmelanoma skin cancers

Study Design Dose / regimen Treatment Control RR [95% CI] Improvement NNT Weight
ONTRAC (Chen) 2015 note DB-RCT Nicotinamide 500 mg twice daily — — 0.77 [0.62–0.96] 23% 2 100%

RR < 1 favors treatment for outcomes where lower is better. Rows in gray have a confidence interval crossing 1 (individually inconclusive). “~” marks effects reported as OR/HR and treated as RR-approximations. “excl” = excluded from pooling (e.g. reviews).

Notes & interpretation

  • ONTRAC (Chen) 2015—New nonmelanoma skin cancers (primary). Rate ratio from 23% lower (95% CI 4-38), P=0.02. Control rate 2.4 lesions/person/12 mo; NNT is per cancer prevented over 12 months.

Background

Nicotinamide (vitamin B3) aids DNA repair and reduces UV immunosuppression. The phase 3 ONTRAC trial randomized 386 high-risk patients (≥2 prior nonmelanoma skin cancers) to nicotinamide 500 mg twice daily or placebo for 12 months. The effect was not maintained after stopping and is not established in average-risk people.

Topic methodology & caveats

Rate ratios from ONTRAC's reported relative differences, converted to risk ratios; the control lesion rate is the NNT baseline. Actinic keratoses also fell (13% at 12 months) but lacked a reported CI, so are not encoded. Single trial (n=386).

Studies